Golf-ball-cover casting molds with self-centering mold-cavity inserts

ABSTRACT

Molds are disclosed for forming golf-ball covers by casting. An exemplary mold includes first and second support members that are placeable in face-to-face opposition to each other. At least one respective mold-cavity insert, defining a respective hemispherical cavity, is mounted to each support member. The mold-cavity insert is floatable in at least three (e.g., x, y, z) degrees of freedom relative to the respective support member. Each mold-cavity insert on the first support member is in face-to-face opposition to a respective mold-cavity insert on the second support member whenever the support members are in face-to-face opposition to each other, such that the respective hemispherical cavities of each opposing pair of inserts form respective spherical ball-cover cavities. A respective z-direction bias is associated with each mold-cavity insert. Also, a respective self-centering device is associated with each opposing pair of inserts. The self-centering device urges movement of at least one mold-cavity insert of the opposing pair in any of at least three degrees of freedom as required to center the mold-cavity inserts of the opposing pair with each other.

FIELD

This disclosure pertains to, inter alia, molds used for manufacturinggolf balls. More specifically, the disclosure pertains to molds used forcasting the outer layer (“cover”) of golf balls.

BACKGROUND

Golf balls have undergone substantial evolution since the early days ofthe game. A modern golf ball 100 (see FIG. 7) is made with multiplelayers, including an outer layer 102 called a “cover” and an inner body104 called a “core.” Many modern golf balls have at least one additionallayer, called a “mantle” 106, situated concentrically outside the core104. The cover 102 is typically formed around the mantle 106 so that thecover is concentric with the mantle and the mantle and core are sealedinside the cover. For purposes of description herein, the term “core” isused generally herein to denote the portion of a golf ball locatedinside the cover and providing the surface on which the cover is formed,regardless of whether the core comprises one or more layers.

Conventional techniques used for forming the cover include casting,compression molding, and injection molding. The surficial dimples areformed at the same time as the cover. Injection molding is usually usedfor forming covers of thermoplastic materials. Compression molding isused for forming covers of polyisoprene (e.g., “balata” or gutta percha)and of certain polyurethane materials. Casting is usually used forforming covers of a thermoset material such as polyurethane, which isformed by reaction of diisocyanate, polyol, and polyamine.

Injection molding is usually performed using a mold body comprising twomold halves. Each mold half defines at least one hemispherical cavitythat, when brought together with the corresponding hemispherical cavityin the other mold half, form a respective spherical ball cavity. Thehemispherical cavities include retractable pins that center the core inthe cavity to ensure that the cover to be formed will be concentric withthe core and have substantially uniform thickness. After placing thecore in the mold, the mold is closed and a liquid thermoplastic materialis injected under high pressure and temperature around the core in thecavity. The pins retract into the mold halves before the thermoplasticmaterial filly envelops the core. As the pins retract, the thermoplasticmaterial fills the spaces previously occupied by the pins. Thethermoplastic material is then allowed to cure filly and the ball isremoved from the mold. Examples of injection molding of ball covers arediscussed in U.S. Pat. Nos. 5,112,556 and 5,201,523.

Compression molding is performed by placing two compliant cover “blanks”around a core. Each blank is configured to become, by high-pressuremolding, a respective half of the cover. The core with blanks in placeis placed in a ball cavity formed by bringing together two mold halvesthat define respective hemispherical cavities. During molding, the moldheats (and thus softens), compresses, and urges the blanks tightlyaround the core at high pressure. The high pressure also seals the twoblanks together around the equator of the ball. The ball is allowed tocool and then removed from the mold. See, e.g., U.S. Pat. No. 3,989,568to Isaac and U.S. Pat. No. 3,130,102 to Watson et al.

Casting (also called “cast-molding”) is performed in a ball cavityformed by bringing together two mold halves that define respectivehemispherical cavities. Casting is especially suitable for forming thecover of a thermoset material. A precise amount of liquid thermosetresin is introduced into the hemispherical cavities and partially cured(“gelled”). The core is placed in the hemispherical cavity of one moldhalf and supported by the partially cured resin. The second mold half isplaced relative to the first mold half to enclose the core and resin inthe resulting ball cavity. As the mold halves are brought together, theresin flows around the core and forms the cover. The mold body is heatedbriefly to cure the resin, then cooled for removal of the ball from themold body. Advantages of casting are that it achieves substantialuniformity of cover thickness without having to use centering pins, andit can be performed at a much lower pressure inside the mold thaninjection molding or compression molding. Indeed, casting can beperformed at substantially zero gauge pressure.

Since all three cover-molding techniques utilize, per ball, twohemispherical cavities that are brought together to form a sphericalball cavity, there is concern with events occurring at the “partingline” during molding. The parting line is represented as an equatorialline on the ball at which the two hemispherical cavities came together,more specifically where the “parting surfaces” of the opposing moldhalves came together. Certain problems with the hemispherical cavitiesor with the parting surfaces, such as “offset” (axial mis-registrationor axis-angular mismatch, roundness mismatch, or diametrical mismatch)of the hemispherical cavities with respect to each other or variationsin the width of the parting line around the equator, is usuallymanifested as a corresponding anomaly on the ball cover formed in themold. Example anomalies include excess equatorial “step,” excess widthof flashing, excess thickness of flashing, and unequal width orthickness of flashing around the ball. Because of their adverse impacton ball trajectory during play and their objectionable appearance, theseanomalies are usually removed by the manufacturer, which requires thatthe manufacturer include one or more post-molding manufacturingprocesses such as localized buffing or grinding. In general, the morepronounced the surficial anomaly, the more extensive (and costly) thepost-molding buffing or grinding process. The required buffing orgrinding can be of such magnitude that their effects on the ball surfaceare aesthetically objectionable and/or interfere with ball trajectory.

Ball-cover molds are usually used many times, and changes in the partingline can occur with repeated use of a mold. For example, axialmis-registration (side-to-side shift) or axis-angular mismatch of themold halves with each other can occur and/or progress with repeated useof the mold. Unless strict quality control is exercised, such drifts canresult in an out-of-control process that produces an unacceptable numberof reject product. Unfortunately, correcting this problem usually meansreplacing the mold with a new one, and new cover molds are veryexpensive.

For manufacturing large numbers of golf balls quickly, manufacturersautomate the cover-forming process as much as possible, and use covermolds configured to cover multiple golf balls simultaneously. To thisend, the cover molds typically define multiple ball cavities (e.g., fouror eight). To provide some correction of mis-registration of mold halveswith each other, some conventional cover molds are spring-loaded.However, the resulting correction is usually not ideal for each of themultiple ball cavities defined by the mold, especially since dimensionalshifts can occur in one ball cavity relative to another in the samemold.

SUMMARY

Various problems of conventional devices and methods, as summarizedabove, are addressed by various aspects of the invention as disclosedherein.

One aspect concerns mold-halves for golf-ball-cover casting molds. Anembodiment of such a mold-half comprises a support member, a mold-cavityinsert, a mounting, and a self-centering device. The mold-cavity insertdefines a substantially hemispherical ball-cover cavity. The mountingcouples the mold-cavity insert to the support member and providesfloatability of the mold-cavity insert, relative to the support member,in multiple degrees of freedom (for example, and not intending to belimiting, in x, y, and z degrees of freedom). The self-centering deviceis associated with the mold-cavity insert and is engageable with amating mold-cavity insert on a facing support member to urge movement ofthe mold-cavity insert in the degrees of freedom as required to centerthe mold-cavity insert with the mating mold-cavity insert.

Desirably, the mold-half includes a bias (desirably a z-direction bias,wherein x- and y-directions define major surfaces of the supportmember). The bias facilitates positioning of the mold-cavity relative tothe support member without interfering significantly with thefloatability of the mold-cavity insert relative to the support member.The bias desirably is a z-direction bias (relative to x- andy-dimensions of the support member). An example bias is a compressionspring such as, but not limited to, a “wavy washer.”

The support member can comprise or be configured as a plate defining abore. With such a support member, the mold-cavity insert can be situatedin the bore with sufficient clearance to provide the floatability of themold-cavity insert in the multiple degrees of freedom.

The self-centering device can have any of various configurations suchas, but not limited to, pin-and-hole or mutually engaging slopedsurfaces.

Another aspect of the invention concerns molds for casting golf-ballcovers. An embodiment of such a mold comprises first and second supportmembers that are placeable in face-to-face opposition to each other. Atleast one respective mold-cavity insert, defining a respectivesubstantially hemispherical cavity, is mounted to each support member.The at least one mold-cavity insert is floatable in multiple (e.g., x,y, and z) degrees of freedom relative to the respective support member.Each mold-cavity insert on the first support member is in face-to-faceopposition to a respective mold-cavity insert on the second supportmember whenever the support members are in face-to-face opposition toeach other such that the respective substantially hemispherical cavitiesof each opposing pair of inserts form respective spherical ball-covercavities. A respective z-direction bias is associated with eachfloatable mold-cavity insert. Associated with each opposing pair ofinserts is a self-centering device that urges movement of at least onemold-cavity insert of the opposing pair in any of the multiple degreesof freedom as required to center the mold-cavity inserts of the opposingpair with each other.

According to another aspect, methods are provided for casting a cover ona golf ball. An embodiment of such a method comprises mounting at leastone opposable pair of first and second mold-cavity inserts, each insertdefining a respective substantially hemispherical cavity for casting arespective half of a cover and each insert defining a respective partingsurface, to respective support members in a manner providing at leastone of the first and second mold-cavity inserts with floatability in atthree degrees of freedom relative to the respective support member. Themold-cavity inserts of the opposable pair are provided with respectiveself-centering devices. A castable resin and core are added to thehemispherical cavities of the mold-cavity inserts of each opposablepair. The support members are moved to position the mold-cavity insertsof the opposable pair face-to-face with each other. The parting surfacesof the face-to-face mold-cavity inserts are brought into mutual contactsuch that the hemispherical cavities form a ball-cavity enclosing theresin and core. As the parting surfaces are brought into mutual contact,the self-centering devices of the face-to-face mold-cavity inserts aremutually engaged with each other to center the inserts with each other.The resin is then cured to form a covered golf ball. The mold-cavityinserts opened and the covered golf ball is removed from the ballcavity.

Engaging the self-centering devices desirably comprises automaticallydisplacing, as required, at least one of the face-to-face mold-cavityinserts according to its x, y, z degrees of freedom, relative to theother insert and relative to the support members, to center themold-cavity inserts with each other.

The foregoing and additional features and advantages of the inventionwill be more readily apparent from the following detailed description,which proceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a representative embodiment of a moldhalf used for simultaneously casting covers on eight golf balls. Each ofthe eight large bores in the depicted plate accepts a respectivemold-cavity insert; only one mold-cavity insert is shown, in an explodedmanner. For casting, the depicted mold half is used with a mirror-imagemold half (not shown) placed face-to-face with the depicted mold half toform a mold body defining eight ball cavities.

FIG. 2 is an elevational section of a mold-cavity insert situated in itsrespective bore in the plate of the mold half shown in FIG. 1.

FIG. 3 is an elevational section of portion of a mold body comprisingtwo mold halves, configured as shown in FIGS. 1 and 2, situatedface-to-face for casting. A golf ball is shown in each of the depictedball cavities.

FIG. 4(A) is an elevational section of a first embodiment of amold-cavity insert, including centering means.

FIG. 4(B) is a plan view of the mold-cavity insert of FIG. 4(A).

FIG. 5(A) is an elevational section of a second embodiment of amold-cavity insert, including centering means.

FIG. 5(B) is a plan view of the mold-cavity insert of FIG. 5(A).

FIG. 6 is an elevational section of a conventional mold-cavity insert.

FIG. 7 is a section of a conventional golf ball, showing a core, mantle,and cover. The core and mantle collectively constitute a “core” as thisterm is generally used herein. The surface of the core is sealinglycovered by the cover.

DETAILED DESCRIPTION

The invention is described in the context of representative embodimentsthat are not intended to be limiting in any way.

As used in this application and in the claims, the singular forms “a,”“an,” and “the” include the plural forms unless the context clearlydictates otherwise. Additionally, the term “includes” means “comprises.”Further, the term “coupled” encompasses any of various ways in which onething is linked, mounted, or attached to, and does not exclude thepresence of intermediate elements between the coupled things.

In the following description, certain terms may be used such as “up,”“down,”, “upper,” “lower,” “horizontal,” “vertical,” “left,” “right,”and the like. These terms are used, where applicable, to provide someclarity of description when dealing with relative relationships. But,these terms are not intended to imply absolute relationships, positions,and/or orientations. For example, with respect to an object, an “upper”surface can become a “lower” surface simply by turning the object over.Nevertheless, it is still the same object.

Mold bodies, as disclosed herein, for casting covers on golf ballsgenerally comprise two mold halves each comprising a respective “plate”or analogous support member. Each plate holds at least one respectivemold-cavity insert mounted thereto. Each mold-cavity insert defines arespective substantially hemispherical cavity having surficial features(e.g., dimple convexities) corresponding to desired features to beformed in a ball cover formed in the mold. In preparation for casting aball cover, opposing mold-cavity inserts are brought together inface-to-face contact so that their respective hemispherical cavitiesform a spherical ball cavity in which the ball cover can be cast.

To facilitate their being brought together, the two mold halves can behinged to each other in a book-like or clamshell manner and pivoted toopen or close the ball cavities. Alternatively, one or both mold halvescan be mounted on linear slides by which the mold halves are broughttogether face-to-face in a linear manner. Further alternatively, atleast one of the mold halves can be mounted on a robotic device thatbrings the two mold halves together by any of various motions. Furtheralternatively, the mold halves can simply be configured to be moved andbrought together by hand.

Each mold-cavity insert on one mold half corresponds to a respectivemold-cavity insert on the other mold half. As a result, the two moldhalves of the mold body comprise at least one (desirably multiple, suchas four or eight) pair of opposing mold-cavity inserts that, whenbrought together, cooperate with each other in defining the respectiveball cavity. To define the ball cavity fully in a manner suitable forcasting a ball cover, the respective “parting surfaces” of the opposingmold-cavity inserts are brought into full contact with each other.

With respect to each pair of opposing mold-cavity inserts, at least onemold-cavity insert is mounted to its plate in a manner providing atleast three degrees of freedom (x, y, z) of motion of the insertrelative to the plate. Thus, the mold-cavity insert “floats” relative tothe plate and relative to its opposite mold-cavity insert. Desirably,both opposing mold-cavity inserts are floating, each with its ownindependent x, y, z degrees of freedom, relative to the respectiveplates.

Opposing mold-cavity inserts also include self-centering devices thatautomatically engage with each other as the mold-cavity inserts arebrought together to form the ball cavity. The self-centering devices ofopposing mold-cavity inserts are progressively engaged as themold-cavity inserts are brought closer together face-to-face, and arefully engaged when the parting surfaces of the inserts are in fullcontact with each other. Thus, the opposing mold-cavity insertsautomatically self-center with each other, as required, as the moldhalves are bought together for casting. Whereas the self-centeringdevices provide the impetus for this motion, as required, any actualmotion that results is made possible by the x, y, z degrees of freedomof motion of the mold-cavity inserts relative to the respective plates.Each opposing pair of mold-cavity inserts of the mold body exhibits thisself-centering motion, as needed, and such motion of one opposing pairof mold-cavity inserts is independent of such motion of any otheropposing pair of mold-cavity inserts of the mold body. Theself-centering movability of each opposing pair of inserts isindependent of the manner in which the mold halves are brought together.Furthermore, the self-centering movability ensures that opposing pairsof mold-cavity inserts remain aligned with each other over the usefullife of the mold. As the mold halves undergo wear with repeated use, theself-centering movability of the mold-cavity inserts substantiallyself-corrects misalignments of the inserts that otherwise wouldinevitably result from such wear.

Also desirably, at least one mold-cavity insert (of an opposing pairthereof) includes a bias. Thus, upon being urged into a particularposition by its self-centering device, the mold-cavity insert normallytends to remain in the position until or unless urged into a newposition by the self-centering device. A desired bias is in thez-direction relative to the plate, as achieved by, for example, acompression spring. This bias is described in more detail later below.

Representative Embodiment of Mold Half

A representative embodiment of a mold half 10 is shown in FIG. 1. Acomplete mold body comprises two mold halves 10 that are mirror-imagesof each other. When brought together face-to-face, as describedgenerally above, the two mold halves 10 define molds for forming coverssimultaneously around multiple golf balls. This particular embodiment isconfigured to form covers around eight golf balls simultaneously.

The depicted mold half 10 comprises a plate 12 into which eightmold-cavity inserts 14 are mounted in respective bores 16 defined in theplate 12 (only one mold-cavity insert 14 is shown). Each mold-cavityinsert 14 defines a respective hemispherical cavity 48. Each mold-cavityinsert 14 is mounted to the plate 12 using a respective spring-washer 18and a respective snap-ring 20. A particularly desirable type ofspring-washer 18 is a so-called “wavy” spring-washer that, in contrastto a conventional flat washer, has a waviness or rippled configurationaround its circumference that makes the washer compressible in its axial(z) direction. Each bore 16 comprises a smaller-diameter portion 22 anda larger-diameter portion 24 that form a shoulder 26 on which thespring-washer 18 rests.

Desirably, the plate 12 and mold-cavity inserts 14 are made of extremelyrigid and stable metals or other suitable materials capable of beingrepeatedly subjected to molding conditions. The mold-cavity inserts 14desirably are made of an alloy of stainless steel (e.g., 304SS or 316SS)for maximum inertness, thermal stability, and surface quality. The plate12 can be made of stainless steel, but alternatively can be made ofanother suitable metal or combination of metals. An example is a layerof aluminum alloy sandwiched between two layers of titanium alloy, whichhas less mass than stainless steel and thus is more easily handled. Thistitanium sandwich adds appropriate hardness and wear resistance whereneeded (e.g., in the bores 16), despite its lower mass. Hence, thetitanium sandwich is more desirable than making the plate 12 entirely ofaluminum alloy. Another candidate material for the plate 12 is a ceramicmaterial. An example thickness of the plate 12 is 1.5 inch.

Turning now to FIG. 2, a mold-cavity insert 14 is shown in section, asmounted in its respective bore 16 in the plate 12. Visible are thesmaller-diameter portion 22, the larger-diameter portion 24, theshoulder 26, the spring-washer 18, and the snap-ring 20. The mold-cavityinsert 14 comprises a narrower cylindrical portion 28 and a widercylindrical portion or flange 30. The portions 28, 30 define a shoulder32. The narrower cylindrical portion 28 slip-fits (with some diametricalclearance as discussed later below) into the smaller-diameter portion 22of the bore 16, and the flange 30 slip-fits (with some diametricalclearance as discussed later below) into the larger-diameter portion 24of the bore. The spring-washer 18 is situated between the shoulders 26and 32 and creates a variable gap 34 therebetween as a result of thespring-washer's compressibility in the z-direction. The “lower” end 36of the narrower cylindrical portion 28 defines a gland 38 into which thesnap-ring 20 fits. I.e., the snap-ring 20 has an inside diameter thatfits in the gland 38 and an outside diameter greater than the diameterof the smaller-diameter portion 22 and the diameter of the narrowercylindrical portion 28. Thus, the snap-ring 20 contacts the “lower”surface 40 of the plate 12. The gland 38 is situated so that, wheneverthe snap-ring 20 is in the gland, the spring-washer 18 applies aprescribed amount of compliant tension, in the z-direction, to themold-cavity insert 14 relative to the plate 12.

Referring further to FIG. 2, the “upper” surface 42 of the plate 12 isshown. The larger-diameter portion 24 of the bore 16 extends depth-wisefrom the upper surface 42 into the plate 12 and receives the flange 30.The “upper” surface 44 of the flange 30 is shown, slightly recessedbelow the upper surface 42. Thus, the flange 30 has a parting surface 46that is “prouder” than the upper surfaces 42, 44. I.e., the partingsurface 46 in FIG. 2 is slightly higher than the surfaces 42, 44. By wayof example, the parting surface 46 is prouder by 0.080 inch than theupper surfaces 42, 44.

As noted, the mold-cavity insert 14 defines a hemispherical cavity 48,which can be seen in FIGS. 1 and 2. The surface of the hemisphericalcavity 48 includes multiple small, shallow, convexities 50 that definecorresponding dimples in the surface of the ball cover during casting.As two mold halves 10 are brought together face-to-face, mold-cavityinserts 14 of opposing pairs thereof contact each other at their partingsurfaces 46. Hence, each pair of inserts forms a respective sphericalball cavity in which a respective ball cover is cast.

The mold-cavity insert 14 has three degrees of freedom of movabilityrelative to the plate 12, namely movability in the x-, y-, andz-directions. Movability of the insert 14 in the x-y plane is achievedby providing the smaller-diameter portion 22 and larger-diameter portion24 of the bore 16 with respective excess diametrical clearances 35, 37relative to the narrower cylindrical portion 28 and flange 30,respectively. An example clearance 35, 37 is 0.010 inch or less, or0.005 inch or less, or 0.003 inch or less. Thus, the mold-cavity insert14 has a small amount of “float” in the x-y plane (i.e., has two degreesof freedom of motion in that plane). Movability of the insert 14 in thez-direction is independent of movability in the x-y plane, and is aresult of the compliant z-direction compressibility provided to theinsert by the spring-washer 18, relative to the plate 12. The“compliant” nature of this insert compressibility is provided by thez-direction compressibility of the spring-washer 18 (e.g., acompressibility of 0.036 inch). Thus, the mold-cavity insert 14 also hasa small amount of “float” in the z-direction. By way of example, and notintending to be limiting in any way, if the parting surface 46 isprouder by, nominally, 0.080 inch than the upper surfaces 42, 44, andthe spring-washer 18 has an axial compressibility of 0.036 inch, thenthe minimum “proudness” of the parting surface 46 is 0.044 inch.

The snap-ring 20 in its gland 38 and in contact with the lower surface40 limits the amount of upward motion permitted to the mold-cavityinsert 14 relative to the plate 12. The maximum z-directioncompressibility of the spring-washer 18 poses a limit to the amount ofdownward motion permitted to the insert 14 relative to the plate 12.Desirably, the position of the snap-ring 20 in the z-direction is suchthat, at the upward-motion limit of the insert 14 relative to the plate12, the spring-washer 18 is still under slight compression, which servesto maintain the position of the insert in the x-y plane. This alsoensures that, at the moment of mutual contact of the parting surfaces 46of opposing inserts 14 being brought together for casting, the insertsare still under the effect of slight compression of the spring-washer18.

Returning to FIG. 1, the plate 12 also defines bores 52 used forreceiving respective clamping pins (not shown) used for holding twoplates (with mold-cavity inserts 14) together face-to-face. The plate 12also defines bores 54 used for receiving respective alignment pins (notshown) used, for aligning two mold bodies 10 (with respectivemold-cavity inserts 14) together face-to-face. FIG. 1 also shows that,with respect to each bore 16, the larger-diameter portion 24 desirablyincludes a flat 56 that engages a corresponding flat 58 on the edge ofthe flange 30 of the respective mold-cavity insert 14. With mutualengagement of the flats 56, 58, the mold-cavity inserts 14, while beingallowed to float in the x-, y-, and z-directions, are substantiallyconstrained from rotating in their respective bores 16 about theirrespective z-axes (i.e., constrained with respect to θ_(z) motion).

An assembly 60 of two opposing mold halves 10 with mated mold-cavityinserts 14 is shown in FIG. 3. The mold-cavity inserts 14 are mated attheir respective parting surfaces 46. The hemispherical cavities 48 ofeach mated pair define a respective spherical ball cavity 62. Duringcover-molding, each ball cavity 62 receives a respective core 64 and arespective amount of resin (e.g., polyurethane precursor) sufficient toform a cover 66 of uniform thickness completely around the core.

Schematically depicted in FIG. 3 is a coupling device 88 configured atleast to bring the two mold bodies 10 together face-to-face. Thecoupling device 88 can be, for example, a hinge or analogous pivotingdevice by which the mold bodies 10 come together and open in the mannerof a book. Alternatively, the coupling device 88 can be a linear slideor analogous structure that brings the mold bodies 10 together linearly.The coupling device 88 also can provide mechanical support for the moldbodies 10 especially when the mold bodies are in face-to-face contact asshown in FIG. 3

Although not shown in FIGS. 1 or 2 (but see items 90 in FIG. 3), nearthe parting surfaces 46 of each mold-cavity insert 14 are respectiveself-centering devices 90 for achieving (in view of the x-y-z float ofthe inserts 14) substantial alignment (including centering) of theinsert with its opposing counterpart insert in the opposing plate 12. Inone embodiment, as shown in FIGS. 4(A)-4(B), the self-centering devicescomprise multiple tapered pins 68 and tapered holes 70 arranged on abolt circle 72 that is concentric with but outboard of the partingsurface 46. The profile of the pins 68 desirably conforms to the depthprofile of the holes 70. The pins 68 and holes 70 desirably are arrangedin alternating order around the bolt circle 72 on each insert 14. Atleast two pins 68 and two holes 70 are provided on each mold-cavityinsert 14 such that the holes 70 on one insert 14 receive correspondingpins 68 on the facing insert whenever the inserts 14 come together formolding. Note that engagement of the pins 68 with respective holes 70still allows the parting surfaces 46 on facing inserts 14 to contacteach other during use for molding. Note also that, with each mold-cavityinsert 14, mutual engagement of the flats 56, 58 keeps the pins 68 andrespective holes 70 in substantial θ_(z) alignment with each other.

In some embodiments the multiple pins 68 and holes 70 are arranged inalternating order around the bolt circle 72. In alternativeconfigurations, especially those having more than four pins and holesper mold-cavity insert 14, the order of pins and holes can be changed,such as two pins 68 followed by two holes 70, and so on, around the boltcircle 72. The minimum number of pins and holes around the circle 72 isat least three; a total of four (as shown) is more desirable. Otherpractical numbers are six and eight. In other alternativeconfigurations, instead of pins and holes being provided on each insert14, each insert can have either all pins 68 or all holes 70 arrangedaround its bolt circle 72 (with the opposing insert having all holes 70or all pins 68, respectively). In any event, as opposing mold-cavityinserts 14 come together for molding, the pins 68 on one insert entercorresponding holes 70 on the facing insert as their respective partingsurfaces 46 come into mutual contact.

As facilitated by the taper of the pins 68 and holes 70 and by the x-y-zfloat of the inserts 14, the respective inserts of each opposing pairself-align with each other. I.e., if one insert 14 of the pair isslightly misaligned or not centered with its opposing insert, entry ofthe tapered pins 68 of one insert into respective holes 70 of theopposing insert urges appropriate movement, in the x-y plane, of one orboth inserts of the pair relative to each other and relative to therespective plates 12 to restore mutual alignment of the inserts. Also,full contact of the parting surfaces 46 of opposing inserts 14 isassured by compensating motion of one or both inserts against theircompressibility in the z-direction. Each opposing pair of mold-cavityinserts 14 self-aligns in this manner, independently of the other pairsof inserts mounted in the same plates 12. Self-alignment occurs even ifthe opposing plates 12 have become misaligned with each other such asthrough extended use or wear.

For comparison, a conventional mold-cavity insert 200 for castinggolf-ball covers is shown in FIG. 6. The depicted insert 200 comprises anarrower cylindrical portion 202, a flange 204, a shoulder 206, aparting surface 208, and a snap-ring gland 210. The mold-cavity insert200 defines a hemispherical cavity 212. The mold-cavity insert 200 fitsinto a corresponding bore in a plate (not shown), but not in a mannerthat provides any compressibility of the insert in the z-direction, notin a manner that provides x-y-z float of the insert in the plate, andnot in a manner that achieves self-centering of opposing mold-cavityinserts in facing mold halves.

An alternative embodiment of a self-centering device, shown in FIGS.5(A)-5(B), comprises a circumferential projecting edge 80 that extendsin the z-direction. The projecting edge 80 is concentric with butoutboard of the parting surface 46. The projecting edge 80 comprisesportions 82 a, 82 b having respective sloped sides 84 a, 84 b. Thesloped sides 84 a face radially inward, and the sloped sides 84 b faceradially outward. On opposing mold-cavity inserts 14, the inward-slopedsides 84 a on one insert engage respective outward-sloped sides 84 b onthe opposing insert. Engagement of the sloped sides 84 a, 84 b withtheir respective counterparts on facing inserts 14 still allows contactof the parting surfaces 46 on the facing inserts 14 with each otherduring use for molding. Note also that, with each mold-cavity insert 14,mutual engagement of the flats 56, 58 keeps the sloped sides 84 a, 84 bin substantial rotational alignment with each other.

For engagement, it is not necessary that the slopes on opposing slopedsides 84 a, 84 b be identical, since self-alignment of the opposingmold-cavity inserts 14 is achievable in either event. The portions 82 a,82 b in each circumferential edge array 80 desirably are separated fromeach other by a gap 86. The number of portions 82 a, 82 b is shown aseight per insert 14, but this number is not intended to be limiting forachieving self-alignment of opposing inserts.

As facilitated by the slopes of the sloped sides 84 a, 84 b and by thex-y-z float of the mold-cavity inserts 14, facing inserts automaticallyself-center and thus align with each other as the inserts are beingbrought together face-to-face. I.e., if one insert 14 is slightlymisaligned with its mating insert 14, engagement of the portions 82 a,82 b with each other on facing inserts urges appropriate movement, inthe x-y plane, of one or both inserts relative to each other andrelative to the respective plates 12 to restore mutual alignment of theinserts. In a mold body comprising two opposing mold halves 10, eachfacing pair of mold-cavity inserts 14 self-centers in this manner.Self-centering of each opposing pair of inserts 14 occurs independentlyof the other inserts mounted in the same plates 12, and occurs even ifthe opposing plates 12 are not exactly aligned with each other. As inthe embodiment of FIGS. 4(A)-4(B), this self-centering of inserts 14continues even in worn plates 12 that are misaligned with each other.

In an exemplary casting process, a prepolymer resin (e.g., diisocyanate,polyol, and a colorant) is prepared. A curing agent (e.g., polyamine) isadded and the resulting mixture is dispensed into each of themold-insert cavities in a first mold half. The mixture is allowed toreact in the cavities for a time required for the mixture to achieve apartial cure (“semi-gelled” state). Within the partial-cure time, a coreis suspended in each cavity. The partial cure is sufficient to supportthe core without having to use an appliance (e.g., centering pins) tohold the core. The mixture is also dispensed into each of themold-insert cavities in a second mold half. The first mold half isinverted, placed over the second mold half, and brought together withthe second mold half to form respective ball cavities. Details of thiscasting process are set forth in U.S. Pat. No. 7,244,384, incorporatedherein by reference.

Although the embodiments described above utilize a wavy spring-washer 18to provide compressibility of the mold-cavity insert 14 relative to theplate 12 in at least the z-direction, it will be understood that othertypes of biasing devices alternatively could be used. For example, thewavy spring washer 18 can be replaced with a conventional compressioncoil-spring. As another example, multiple individual springs can bepositioned at respective positions between the surfaces 26, 32 toprovide, collectively, the desired z-direction bias of the insert 14relative to the plate 12. Advantages of the wavy spring-washer 18 arethat it is very simple, reliable, and capable of providing a strong biasforce in the z-direction over a short distance.

It is not necessary that both mating mold-cavity inserts have arespective wavy spring or other biasing device. In some embodiments,self-alignment of opposing mold-cavity inserts with each other can beeffectively achieved if one of the mating mold-cavity inserts has abiasing device. Indeed, one of the mating mold-cavity inserts can befixed while the other is floating and includes a biasing device.

With respect to mating mold-cavity inserts, floatability in at leastthree degrees of freedom of at least one relative to the other isdesirable. In many embodiments, this floatability is in x, y, and zdegrees of freedom. These particular degrees of freedom are not intendedto be limiting. For example, other embodiments may have floatability inany three or more of the following degrees of freedom: x, y, z, θ_(x),θ_(y), θ_(z).

Also, although the embodiments described above utilize a snap-ring 20for holding a mold-cavity insert 14 in its respective bore 16 in theplate 12, it will be understood that other types of fastenersalternatively can be used. For example, the snap-ring 20 can be replacedwith one or more pins, bolts, or the like. An advantage of the snap-ring20 is that it provides its intended functions with the need to use onlya single, simple, and highly reliable component.

Golf-ball covers formed using the apparatus and methods discussed aboveare not necessarily flashless, and obtaining flashless balls is not anobjective of the associated casting methods. Since the casting isperformed at substantially zero gauge pressure, and since the partingsurfaces of opposing mold-cavity inserts are in full contact with eachother against the z-direction bias provided by the spring-washer, theamount of flash usually left on the ball after casting tends to be low.Also, as a result of the mold-cavity inserts being self-centering withrespect to each other, whatever flash is formed tends to besubstantially uniform around the ball. This flash is easily removed bybuffing or the like. This is in contrast to conventionalinjection-molding and compression-molding techniques and apparatus that,due in part to the very high temperatures and pressures that arerequired, tend to form substantial but differing amounts of flash thatis difficult and time-consuming to remove.

Whereas the invention has been described in connection with severalrepresentative embodiments, it will be understood that it is not limitedto those embodiments. On the contrary, the invention is intended toencompass all modifications, alternatives, and equivalents as may beincluded within the spirit and scope of the invention, as defined by theappended claims.

1. A mold-half of a golf-ball-cover casting mold, the mold-halfcomprising: a support member extending in x- and y-directions; amold-cavity insert defining a substantially hemispherical ball-covercavity; a mounting coupling the mold-cavity insert to the supportmember, the mounting providing floatability of the mold-cavity insert,relative to the support member, in at least three degrees of freedom;and a self-centering device, associated with the mold-cavity insert,engageable with a mating mold-cavity insert on a facing support memberto urge movement of the mold-cavity insert in any of the at least threedegrees of freedom as required to center the mold-cavity insert with themating mold-cavity insert.
 2. The mold-half of claim 1, wherein the atleast three degrees of freedom comprise x, y, and z degrees of freedom.3. The mold-half of claim 1, further comprising a bias situated betweenthe mold-cavity insert and the support member.
 4. The mold-half of claim3, wherein the bias is a z-direction bias.
 5. The mold-half of claim 4,wherein the z-direction bias comprises a compression spring.
 6. Themold-half of claim 1, wherein: the support member comprises a platedefining a cylindrical bore extending in a z-direction into the supportmember; and the mold-cavity insert is situated in the bore withsufficient diametrical clearance to provide the floatability of themold-cavity insert in the at least three degrees of freedom.
 7. Themold-half of claim 1, wherein the self-centering device comprises atleast one pin and at least one hole.
 8. The mold-half of claim 1,wherein the self-centering device comprises at least one projectionhaving a sloped surface that engages a substantially complementarysloped surface on the mating mold-cavity insert.
 9. A mold for casting agolf-ball cover, comprising: first and second support members that areplaceable in face-to-face opposition to each other; at least onerespective mold-cavity insert, defining a respective substantiallyhemispherical cavity, mounted to each support member so as to provide atleast one mating pair of mold-cavity inserts per mold, the mating pairbeing in face-to-face opposition to each other whenever the supportmembers are in face-to-face opposition to each other such that therespective substantially hemispherical cavities of each mating pair formrespective spherical ball-cover cavities; at least one mold-cavityinsert of each mating pair being floatable in at least three degrees offreedom relative to the respective support member; a respectivez-direction bias associated with the floatable mold-cavity insert; and arespective self-centering device, associated with each mating pair ofinserts, urging movement of at least one mold-cavity insert of themating pair in any of the at least three degrees of freedom as requiredto center the mold-cavity inserts of the mating pair with each other.10. The mold of claim 9, wherein the at least three degrees of freedominclude x, y, and z degrees of freedom.
 11. The mold of claim 9,wherein: both mold-cavity inserts of each mating pair are floatable inat least three degrees of freedom relative to the respective supportmember; and a respective z-direction bias is associated with bothfloatable mold-cavity inserts.
 12. A mold for casting a golf-ball cover,comprising: first and second support members that are placeable inface-to-face opposition to each other; at least one respectivemold-cavity insert, defining a respective substantially hemisphericalcavity, mounted to each support member, the at least one mold-cavityinsert being floatable in at least three degrees of freedom relative tothe respective support member; each mold-cavity insert on the firstsupport member being in face-to-face opposition to a respectivemold-cavity insert on the second support member whenever the supportmembers are in face-to-face opposition to each other such that therespective substantially hemispherical cavities of each opposing pair ofinserts form respective spherical ball-cover cavities; a respectivez-direction bias associated with each mold-cavity insert; and arespective self-centering device, associated with each opposing pair ofinserts, urging movement of at least one mold-cavity insert of theopposing pair in any of the at least three degrees of freedom asrequired to center the mold-cavity inserts of the opposing pair witheach other.
 13. The mold of claim 12, wherein the z-direction biascomprises a compression spring.
 14. The mold of claim 12, wherein the atleast three degrees of freedom comprise x, y, and z degrees of freedom.15. The mold of claim 12, wherein: each support member comprises arespective plate defining respective cylindrical bores for therespective mold-cavity inserts; and each mold-cavity insert is situatedin the respective bore with sufficient x-y and z clearance to providethe floatability of the mold-cavity insert in x, y, and z degrees offreedom.
 16. The mold of claim 15, wherein: each mold-cavity insertcomprises a cylindrical portion and a flange defining respective ashoulder; each bore comprises a cylindrical portion and a respectiveshoulder; the x-y clearance is diametrical clearance of the cylindricalportion of the insert relative to the cylindrical portion of the bore;and the z clearance is determined, at least in part, by clearancebetween the shoulders.
 17. The mold of claim 16, wherein the z-directionbias is situated between the shoulders.
 18. The mold of claim 17,wherein the z-direction bias comprises a spring-washer.
 19. The mold ofclaim 15, wherein, with respect to each opposing pair of mold-cavityinserts, the self-centering device comprises at least one pin on a firstmold-cavity insert and at least one complementary hole on a secondmold-cavity insert of the opposing pair.
 20. The mold of claim 15,wherein, with respect to each opposing pair of mold-cavity inserts, theself-centering device comprises, on a first mold-cavity insert of thepair, at least one projection having a sloped side that engages acomplementary sloped side on a projection of the second mold-cavityinsert.
 21. The mold of claim 15, wherein, with respect to each opposingpair of mold-cavity inserts, each mold-cavity insert comprises arespective parting surface, the parting surfaces being contact surfacesof the mold-cavity inserts of the opposing pair whenever the supportmembers are in face-to-face opposition to each other.
 22. The mold ofclaim 21, wherein, with respect to each opposing pair of mold-cavityinserts, the z-direction bias urges the parting surfaces togetherwhenever the support members are in face-to-face opposition to eachother.
 23. The mold of claim 21, wherein, with respect to each opposingpair of mold-cavity inserts, the respective self-centering deviceassociated with each opposing pair of inserts comprises a first portionadjacent the parting surface of one mold-cavity insert, and a secondportion, complementary to the first portion, adjacent the partingsurface of the other mold-cavity insert.
 24. The mold of claim 15,wherein the first and second support members are coupled together in amanner rendering them placeable in face-to-face opposition to eachother.
 25. The mold of claim 15, wherein each of the first and secondsupport members includes multiple respective mold-cavity inserts.
 26. Amethod for casting a cover on a golf ball, comprising: mounting at leastone opposable pair of first and second mold-cavity inserts, each insertdefining a respective substantially hemispherical cavity for casting arespective half of a cover and each insert defining a respective partingsurface, to respective support members in a manner providing at leastone of the first and second mold-cavity inserts with floatability in atleast three degrees of freedom relative to the respective supportmember; providing the mold-cavity inserts of the opposable pair withrespective self-centering devices; with respect to the mold-cavityinserts of the opposable pair, adding a castable resin and core to thehemispherical cavities; moving the support members to position themold-cavity inserts of the opposable pair face-to-face with each other;bringing the parting surfaces of the face-to-face mold-cavity insertsinto mutual contact such that the hemispherical cavities form aball-cavity enclosing the resin and core; as the parting surfaces arebrought into mutual contact, mutually engaging the self-centeringdevices of the face-to-face mold-cavity inserts with each other tocenter the inserts with each other; curing the resin to form a coveredgolf ball; and opening the mold-cavity inserts and removing the coveredgolf ball from the ball cavity.
 27. The method of claim 26, wherein theat least three degrees of freedom comprise x, y, and z degrees offreedom.
 28. The method of claim 26, wherein engaging the self-centeringdevices comprises automatically displacing, as required, at least one ofthe face-to-face mold-cavity inserts according to its at least threedegrees of freedom, relative to the other insert and relative to thesupport members, to center the mold-cavity inserts with each other. 29.The method of claim 26, wherein providing the mold-cavity inserts of theopposable pair with respective self-centering devices comprisesproviding the inserts with pins and conforming holes that mutuallyengage with each other as the parting surfaces are brought into mutualcontact.
 30. The method of claim 26, wherein providing the mold-cavityinserts of the opposable pair with respective self-centering devicescomprises providing the inserts with sloping surfaces that mutuallyengage with each other as the parting surfaces are brought into mutualcontact.
 31. The method of claim 26, further comprising, with respect tothe opposable pair of mold-cavity inserts, providing at least one of theinserts with a z-direction bias.